In semiconductor device fabrication, a photomask may generally be used as an exposure mask when forming a fine pattern. As a photomask, a phase shift mask is used to enhance resolution of a transcript pattern by giving a phase difference between exposure lights transmitted through the mask. In particular, a halftone phase shift mask has been developed and used as a sort of the phase shift mask.
As illustrated in example FIG. 1A, a method of fabricating a halftone phase shift mask may include forming phase shift layer 102 composed of Mo-silicide oxynitride on and/or over a surface of transparent substrate 100 composed of quartz. Metal layer 104 composed of chromium (Cr) is formed on and/or over phase shift layer 102. First photoresist 106 is coated on and/or over substrate 100 including metal layer 104 and phase shift layer 102. Exposure and development are then performed on first photoresist 106 using a prescribed exposure mask to expose a portion of metal layer 104.
As illustrated in example FIG. 1B, phase shift layer 102 and metal layer 104 are then etched in part by a prescribed etch process using first photoresist 106 as a mask to expose a portion of transparent substrate 100.
As illustrated in example FIG. 1C, after removing first photoresist 106, second photoresist 108 is coated on and/or over transparent substrate 100 including phase shift layer and metal layer 104. Exposure and development are then performed on second photoresist 108 using a prescribed exposure mask such that second photoresist 108 can cover a portion of metal layer 104 only.
As illustrated in example FIG. 1D, a portion of metal layer 104 not covered by second photoresist 108 is etched by a prescribed etch process using second photoresist 108 as a mask. However, such a halftone phase shift fabricating method is complicated since it requires a photoresist coating process and second exposure process to expose the phase shift layer after completion of the first exposure. This, in turn, increases the failure ratio and processing time.